The present invention is applicable in particular, to large-format printers, also known as "plotters", which are intended, in particular, for printing on continuous or sheet-like printing media usually printing paper. These printers are computer-controlled and print on a printing media which is moved through the printer, being acted on by an ink-jet printing cartridge which moves transversely relative to the movement of the printing media.
Printers of this type incorporate detectors for detecting the passage of the printing media in order to obtain therefrom a signal which indicates the presence or absence of the printing media, this signal being used by the printer for many processes in accordance with the programs stored in the electronic control unit of the printer.
Currently, printers which have a detector situated at the input for the printing media on its path towards paper-feed rollers which transport it along its path through the printer are known, the substrate normally being paper either in roll form, that is, continuous paper, or in sheet form. The currently-known devices for detecting the presence of the printing media are mounted in the lower portion of the paper input, that is, the portion which corresponds to the paper-input platen, and have a detector lever which points upwards and can pivot on an intermediate pivot pin upon the passage of the front edge of paper coming from the roll incorporated in the printer itself, or of separately-fed sheets. This system has certain disadvantages, amongst which may be cited: the fact that the lever for detecting the presence of the sheet of paper is affected by oscillations and takes a certain time to stop again owing to natural damping after it has been inclined by the action of the edge of the paper or of the sheet of paper. This is a source of delays in the processes for interpreting the signal in th,e printer and therefore of delay in the processes generated on the basis of the said detection.
Another disadvantage is that, when these printers operate in a manner such that the sheet or roll of paper is guided towards the interior of the printer, being guided around a main roller and passing towards the rear, towards the print region forming, as a whole, a U-shaped loop, the end of the pivoting lever of the paper detector contacts the face which will subsequently receive the printing, which is inadvisable since, in certain cases, the contact of the lever may produce marks on the paper which impair the printing carried out or even render it unusable.